The present invention related to three-dimensional porous structures having selected patterns upon and/or in them. More particularly, the present invention relates to three-dimensional porous structures such as membranes that have a series of one or more patterns of porous and non-porous areas.
Patterned porous structures have been known. In particular, patterned porousmembranes have been used to create membranes having hydrophilic areas separated from each other by a grid like pattern of hydrophobic areas. These membranes have been useful in diagnostic applications and in the collection, culturing, enumeration and identification of microorganisms. Thus, it is desirable in these structures to produce a pattern, which prevents cross talk between the hydrophilic areas so that sample cross contamination is prevented.
U.S. Pat. No. 5,271,839 teaches a process for forming patterns in porous structures. It uses an otherwise non-porous polymeric material which has the desired pattern masked off. It then contacts that material with a solvent that gels the exposed surfaces. The gelled material is then precipitated by exposure to a non-solvent for the polymeric material thereby forming porous structures within the polymeric material in the form of the pattern while the masked areas remain non-porous.
U.S. Pat. No. 5,627,042 teaches a surface modification method in which the surface of a hydrophobic membrane is coated with a cross linked hydrophilic polymer in the shape of a pattern. The entire membrane is first contacted with an appropriate monomer or monomers for hydrophilic coating. Subsequently the hydrophilic pattern is formed by UV initiated polymerization and cross linking of the monomers in selected areas of the membrane by exposing portions of the membrane to the light while masking the other portions from exposure to the light. This process results in a membrane having patterned hydrophilic portions in the areas exposed to the UV light and hydrophobic portions in the area masked from the UV light.
Both of these processes have limitations. For example, the method of the ""839 patent is limited in the materials that may be used as some well known polymeric materials such as PTFE resin are difficult or impossible to solvate and therefore not suitable for the process. Even where a solvent is available, many of these solvents are extremely flammable or toxic making their use difficult and or prohibitive. Likewise, the process of the ""042 patent is limited in its ability to form such structures due to the required UV absorbing characteristics of the selected polymers or the relative ability of the structures to retain the hydrophilic or hydrophobic characteristics. In addition, the products made by these processes have relatively flat surfaces. These flat surfaces facilitate migration of liquid sample between the porous areas as compared to a porous area pattern wherein the porous areas are positioned at a different height than the isolating non-porous areas.
Accordingly, it would be desirable to provide a patterned porous substrate having improved means for isolating porous areas thereof from each other. In addition, it would be desirable to provide such a patterned porous substrate that can be formed from conventional porous membranes in a simple and an inexpensive manner.
The present invention provides new patterned porous substrates and a new method for forming the new patterned porous substrates containing one or more selected patterns which is applicable to all porous structures regardless of their polymeric content, their method of manufacture or their UV absorbing characteristics.
The present invention provides a supported three dimensional patterned porous structure formed with areas of porous material and areas of non-porous material formed in the arrangement of a desired pattern of porous and non-porous areas. The three dimensional patterned porous structure is formed from a sandwich that includes a non-porous layer and at least one porous layer. The three dimensional patterned porous structure is formed by collapsing selected portions of the porous structure in the shape of the desired pattern to render these portions non-porous while the remaining portions of the porous layer structure retain the porous structure and are positioned away from the collapsed non-porous structure. Heat and/or pressure are utilized to collapse the selected porous portions while heat, pressure and apparatus geometry are utilized to position the retained porous structure away from the collapsed non-porous structure. The resulting layer formed from the porous layer is collapsed and fused to the non-porous layer of the original sandwich. The process can be applied to any polymeric porous structure of any pore size such as ultrafiltration or microfiltration membranes made by any process such as by precipitation, track etch, stretching, casting, sintering or extrusion. It may also be used on woven and nonwoven porous materials that are collapsible by a combination of heat and pressure. It may also be used with membrane with entrapped particles, such as chromatography media or the like, which are collapsible by a combination of heat and pressure.